1. Field of the Invention
The present invention relates to an integrated coking and hydroconversion process for upgrading hydrocarbonaceous materials wherein a substantially solids-free coker bottoms stream is slurry hydroconverted.
2. Description of the Prior Art
Much work has been done over the years to convert heavy petroleum feedstock to lighter and more valuable liquid products. One process developed for accomplishing this conversion is fluid coking. In conventional fluid coking, a petroleum feedstock is injected into a fluidized bed of hot, fine, coke particles and is distributed uniformly over the surfaces of the coke particles where it is cracked to vapors and coke. The vapors pass through a cyclone which removes most of the entrained coke particles. The vapor is then discharged into a scrubber where the remaining coke particles are removed and the products cooled to condense the heavy liquids. The resulting slurry, which usually contains from about 1 to about 3 weight percent coke particles, is recycled to the coking reactor. The overhead products from the scrubber are sent to fractionation for separation into gas, naphtha, and light and heavy gas oils.
The coke particles in the reactor vessel flow downwardly to a stripping zone at the base of the reactor where stripping steam removes interstitial product vapors from, or between, the coke particles, as well as some adsorbed liquids from the coke particles. The coke particles then flow down a stand-pipe and into a riser which leads to a burner where sufficient air is injected for burning part of the coke and heating the remainder sufficiently to satisfy the heat requirements of the coking reactor where the unburned hot coke is recycled thereto. Net coke, above that consumed in the burner, is withdrawn as product coke.
Another type of fluid coking employs three vessels: a reactor, a heater, and a gasifier. Coke produced in the reactor is withdrawn and is passed through the heater where a portion of the volatile matter is removed. The coke is then passed to a gasifier where it reacts, at elevated temperatures, with air and steam to form a mixture of carbon monoxide, carbon dioxide, hydrogen, nitrogen, water vapor, and hydrogen sulfide. The gas produced in the gasifier is heat exchanged in the heater to provide part of the reactor heat requirement. The remainder of the heat is supplied by circulating coke between the gasifier and the heater.
Still another type of fluid coking process is a so-called once-thru coking process wherein the bottoms fraction from the scrubber is passed directly to a hydrotreating unit or a slurry hydroconversion unit instead of being more conventionally recycled to extinction. The disadvantage of such a once-thru process is that the bottoms fraction is so laden with fine coke particles that it causes plugging of the hydrotreating unit or it comingles with solid catalyst particles in a catalytic slurry hydroconversion unit to such a degree that it is virtually impossible to separate the catalyst particles for recycle purposes.
The term "hydroconversion" is used herein to designate a process conducted in the presence of hydrogen in which at least a portion of the heavy constituents of a hydrocarbonaceous oil is converted to lower boiling products while simultaneously reducing the concentration of nitrogenous compounds, sulfur compounds and metallic contaminants.
Various U.S. patents teach hydroconversion and coking/hydroconversion processes. For example, U.S. Pat. No. 4,134,825 discloses a catalytic slurry hydroconversion process conducted at a pressure of 500 to 5000 psig at elevated temperatures. The catalyst is produced in the oil feed from a catalyst precursor.
U.S. Pat. No. 3,684,689 discloses fluid coking a residuum at a pressure above 150 psig. The coker bottoms are passed to a hydrocracking zone. The stream passed to the hydrocracking zone is a gas oil (see column 3, line 74 and column 6, lines 72-73).
U.S. Pat. No. 2,614,067 discloses coking a topped crude oil in a fluid coker. A gas oil fraction from a fractionator is used as absorber oil in an absorber. The absorber bottoms, which apparently do not include constituents boiling above 1050.degree. F., is passed to a slurry hydrogenation reactor.
U.S. Pat. No. 3,245,900 discloses coking a residuum and sending the coker distillate to a hydrocracking zone.
U.S. Pat. No. 2,888,393 discloses fluid coking at a pressure of 200 to 2000 psig and hydrogenating the entire coker effluent at a pressure ranging from 200 to 2000 psig.
U.S. Pat. Nos. 4,204,943; 4,178,227; and 4,169,038 disclose combination hydroconversion and coking in which the bottoms portion of the hydroconverted product is used as feed to the coking zone.
U.S. Pat. Nos. 4,569,751 and 4,569,752, which are both incorporated by reference herein, describe an integrated coking/hydroconversion process in which the coker bottoms, including materials boiling above 1050.degree. F., are further converted in a catalytic slurry hydroconversion stage. While such an integrated process has met with a degree of success, its drawback is the difficulties associated with the hydroconversion of solids-laden bottom fractions.
Consequently, there is a need in the art for an integrated coking/hydroconversion process in which the scrubber bottoms fraction is made more desirable as a feed for catalytic slurry hydroconversion and hydroconversion bottoms are made more desirable as a feed for the coking reactor.
All boiling points referred to herein are atmospheric pressure equivalent boiling points unless otherwise specified.